1. Field of the Invention
The present invention relates to a sewing machine detector for detecting, for example, the position of a sewing needle and the speed of the sewing machine. The detector is integral with the drive and control elements of the sewing machine.
2. Description of the Background Art
FIG. 8 shows one conventional sewing machine drive system, as disclosed in Japanese Patent Disclosure Publication No. 38496 (1988), including a sewing machine 1, motor 2, belt 3 for the transmission of rotation, needle section 4, control circuit section 5 for the drive control of the motor 2, detector 6 and power indicating light 100.
FIG. 9 shows, in more detail, an optical fiber type needle position detector of the conventional apparatus disclosed in Japanese Patent Disclosure Publication No. 38496 (1988) which includes a detecting section 6a, an optical fiber cable 6b, a photoelectric translation processing module section 6c, and electrical connectors 6d, 7 for connecting the module section 6c and control circuit section 5.
FIGS. 10 and 11 show, in more detail, the detecting section 6a of the conventional needle position detector shown in FIGS. 9 and 10, including a sewing machine shaft 10, a shaft 11 of the detecting section 6a rotated in engagement with the sewing machine shaft 10, and needle UP position and needle DOWN position detecting reflective discs 12, 13 installed on the shaft 11 for reflecting light from a needle UP position detecting optical fiber 14 and a needle DOWN position detecting optical fiber 15, respectively. FIG. 11 shows a reflecting portion 13a of the reflective disc 13, an optical fiber supporter 16, a light sending optical fiber 15a provided in correspondence with the reflecting portion 13a of the needle DOWN position detecting reflective disc 13, and a light receiving optical fiber 15b provided in correspondence with the reflecting portion 13a of the needle DOWN position detecting reflective disc 13. Though not shown in FIG. 11 (See FIG. 12), a light sending optical fiber 14a and light receiving optical fiber 14b, in correspondence with the reflecting area of the needle UP position detecting reflective disc 12, are also provided and perform the same functions as described above with respect to the light sending optical fiber 15a and light receiving optical fiber 15b.
FIG. 12 shows a module section 6c of the needle position detector including light emitting devices 20, light receiving devices 21, a light sending optical fiber 14a for needle UP position detection, a light receiving optical fiber 14b for needle UP position detection, a light sending optical fiber 15a for needle DOWN position detection, a light receiving optical fiber 15b for needle DOWN position detection, an enclosure 22 of the module section 6c, a circuit board 23 with light emitting devices 20 mounted thereon, electronic components 24 for a signal processing circuit, a circuit board 25 on which electronic components 24 are mounted, and a connector 6d for electrical connection to a control circuit section 5.
The operation of the detector will be described next. First, prior to initiating operation, the positional relationships between the UP and DOWN positions of the sewing machine needle and detector reflective discs 12, 13 must be adjusted and fixed. During operation, power is supplied from the control circuit section 5 via the connectors 7, 6d, and light which has been photoelectrically-translated by the light emitting devices 20 in the module section 6c enters the light sending optical fiber 14a or 15a, reaches the light radiating portion of the detecting section 6a via the optical fiber cable 6b, is reflected by the reflecting portion 12a of the reflective disc 12 or the reflecting portion 13a of the reflective disc 13, is received by the light receiving optical fiber 14b or 15b, returns to the module section 6c again, is photoelectrically-translated by the light receiving devices 21, is waveform-processed by the signal processing circuit 24, passes through the connectors 6d and 7 as an electrical signal, and is transmitted to the control circuit section 5 as a needle UP position or needle DOWN position signal for controlling the sewing machine.
In the conventional detector 6, the optical fibers 14, 15 act to both send and receive light to and from the detecting section 6a mounted in engagement with the sewing machine shaft 10 and including the reflective discs 12, 13 for indicating a sewing machine needle position, i.e., the optical fibers 14, 15 are employed solely for purposes of detection. The photoelectric translation processing module section 6c connected to the control circuit section 5 includes electronic parts, such as the light emitting and receiving devices 20, 21 and signal processing circuit 24, while the detecting section 6a and module section 6c are connected by optical fibers 14, 15 housed in an optical fiber cable 6b. With the conventional arrangement, as described above, the influence of static noise due to the friction of a fabric to be sewn as well as other noise is eliminated. Malfunction is thereby avoided and stable sewing machine operations can be performed.
In the conventional detector, as described above, light 13, sent through the light sending optical fibers 14a or 15a, is reflected by the reflecting portion of the reflective discs 12 or 13 secured to the shaft 11 and is received through the light receiving optical fibers 14b or 15b. However, the reflective discs 12, 13 must withstand constant vibration during the operation of the sewing machine 1. Furthermore, if the bearings supporting the shaft 11 are worn, the shaft 11 vibrates to an even greater extent, causing the optical axes between the optical fibers 14, 15 and the reflecting portions of the reflective discs 12, 13 to change, resulting in an inability to receive predetermined signals.
Also, since the reflecting portions of the reflective discs 12, 13 are curved, they are difficult and expensive to machine.
Further, the rotary reflective discs 12, 13 employed as components for signal detection make the detecting section 6a relatively thick and non-compact.
Further, in the conventional detector, since the light sending optical fibers 14a, 15a and light receiving optical fibers 14b, 15b must be flexed, as shown in FIG. 11, in consideration of the curvatures of the reflective discs 12, 13, significant stress is imposed on the optical fibers 14, 15.
Due to the elasticity of the optical fibers 14, 15, and depending on the degree of curvature of the fibers, there may be a relatively large internal force directing the fibers 14, 15 to return to their original, straight line status, which internal force, as noted above, results in a significant stress in the fibers 14, 15 in the area where the fibers 14, 15 are inserted into the optical fiber supporter. Thus, in combination with the above-mentioned vibration, there is a significant possibility that the optical fiber supporter 16 may fracture.
Furthermore, when the curvature radius is large, the light transmitting percentage of the optical fibers 14, 15 decreases, and the efficiency deteriorates. Consequently, expensive optical fibers are necessary to prevent the above described problems.
The conventional apparatus as shown in FIG. 8 also includes a power indicating light 100 having a light emitting diode and lead wires run through cable 6b to turn on the light emitting diode. As noted above, the optical fibers are only employed for detection purposes. By way of contrast, power is supplied by the control circuit section 5 through regular lead wires run through cable 6b to the power indicating light 100.
Industrial sewing machines are often used in areas where high frequency welders are used, e.g., to seal raincoats, tents, etc. However, since high frequency welders generate high frequency electromagnetic waves of about 27 Mhz to 42 Mhz with outputs of several KW to several tens of KW, the lead wires in cable 6b for the power indicating light 100 can act as antennas thereby receiving the electromagnetic waves and generating an electromotive force. This electromotive force is highly undesirable as it affects the control device 5 and may cause the control device 5 to operate erroneously.